I have been absolutely thrilled about the heat output of the Harman Mark II i recently acquired. I couldn't ask for anything more, and my measly ~1400sq/ft home is heated well beyond it's needs in the coldest of days (near zero one night already). The questions I have had are about partially loading the stove to lower the consumption and heat output. On days when temps outside hit around 40 or more, the stove just puts out way too much heat. With the windows open and draft down to 1/3 turn, it can still hit high 80's/90's in the home if I'm not careful. I can't turn it down any more than that without ending up with large amounts of unburnt coal and just overall poor utilization of fuel.

I tried thinking about this a few ways. Maybe i could weld up a small stainless insert to contain the coal in the middle or to one side, but still leave an arc at the bottom for shaking. For one reason or another, most of my ideas never made it off the drawing board. Without a even bed of coals, the draft wouldn't work and the coal wouldn't burn. So that's when i cam up with the lazy man's solution. I have done this for 5 days straight now without losing the fire since our big snow storm. the home has stayed between 74-77 degrees with the windows shut most of the day and my consumption has dropped to +/- 15lbs a day of nut Blaschak.

I bank the coal against the left side since it seemingly shakes down more thoroughly than the right side does. I leave a thick bed of ash on the right half and actually shovel ash from the pan back into the top, just to keep the bed 3-4 inches deep to block the draft from bypassing the coal i want to burn. I bank the left side all the way to the top of the bricks in the morning and have gotten a 14 hour run out of it so far on average. A little more care needs to be taken when reloading as to not make a mess though. The stove is staying dustier inside and i expected that, but running it this way at 2/3 turn open has yielded exactly the results i have hoped for. The coal consumption is even lower than i expected as well. https://www.dropbox.com/s/n2iyz3yh9t6ob21/2013-02-13%2012.40.48.jpg

Does anyone have any ideas or comments on this for running a stove at a very low heat output? maybe i am doing this the wrong way, but i just couldn't figure out a way to run the bed full width without wasting a load of coal on the edges. Burning this way has allowed me to use every bit of coal since i put unburnt pieces that rolled away back on the pile during reload. It is dirtier than running it normally, but the head output has been perfect. seems to only burn half way into the pile and take all day to reach and ignite the top. going to try and let it go late tonight since it was tended at 4am this morning as a test.

coalkirk wrote:Honestly for your square footage, you should have a mark I. I'm guessing you are using nut coal. Try using pea or a mix of nut and pea.

unfortunately, i have a 2400lbs of nut left. i will go ahead and try and get some pea to mix in though. I know the stove is a bit over sized for my home, but the deal was too good to pass up. it has occurred to me that i may be better off trading down to a good condition Mark I or similar in the off season rather than try to constantly throttle this thing to almost nothing.

Resolute0058.....Depending how your grate system works and connects you may be able to disconnect one grate and only use one instead of two. Now you would only use 1/2 the firebox front or back depending on the grate that is connected. You can leave ash on the fixed grate to block the air in that area. You would have to make sure that the grate your not using will not open and drop ash. Maybe wired or propped some way to stay in place until you want to use the two grates again.

My home is 1600 sq. ft. And have a Mark 1 installed last fall. I thought it would be enough heat. Ok for the living area of 28x30. On a cold day say -14 the living room is only 67 degrees. Stove temp 550 degrees. Other rooms cooler. Old and new windows, some insulation in walls, addict R-40. I found a Mark 3. And will install next fall. I have learn from other coal burners that one can always throttle back but not up. Your situation seems that your home has good Windows's and walls. In my case I would cover one great with a u channel metal. George

Halfing loading your Mark II won't do the job. Do you have a thermometer on the outside of the stove? If so how hot is your stove running as it produces all the heat? How low can you get that temperature and still have your room temperature where you want it? I have my external thermometer on the upper right edge of the load door. It gives me a pretty good idea how the burn is going. I also have light switch plates with a thermometer built in so I know how hot the room is. Don’t worry about trying to reduce the size of your firebox, try reducing the amount of air moving through the coal bed. You’ll get a slower, cooler burn that will reduce your coal usage. With a Mark II you should be able to reduce your stove’s external temperature to 200* or less and not lose your fire. On my stove that’s a 1/3 spin on the spinner. What you want to find is the lowest possible external stove temperature that maintains the burn and the room temperature you want. With my Mark II I need to keep my external stove temperature at 300* or 450* to keep my room temperature at 78* (one full spin of the spinner) with an outdoor temperature of 30*. I suggest keeping a log on what you do to the stove/fire and the results it produces until you know your stove. That way you can refer back and not have to reinvent the wheel each time something is different.

As an earlier poster suggested there is a lot you can do to reduce the heat the stove is producing. Using pea coal or a mixture of pea and nut will slow the burn, cooling the stove and your room. I don’t even mix the pea or nut anymore but rather layer it for the same effect. I’ll have an inch or two of pea on the bottom so my fire is slow in the evening. Then I’ll add a layer of nut so it burns hotter in the colder overnight hours and then I top it off with pea to slow it down again in the morning. You can also slow your burn by not removing all the ash when you shake thereby cutting the air flow through the coal bed. In warmer weather I often let my stove go for 24 hours without shaking it to slow the burn and lower the temperature.

Finding the balance between the stove’s temperature, the outside temperature and the heat you want to produce for the least amount of coal is the art of using a hand fed coal stove and the major factor is the air flow through the coal bed, not the size of the coal bed. I hope this helps, take care, Lisa

Resolute0058 wrote:Does anyone have any ideas or comments on this for running a stove at a very low heat output? maybe i am doing this the wrong way, but i just couldn't figure out a way to run the bed full width without wasting a load of coal on the edges. Burning this way has allowed me to use every bit of coal since i put unburnt pieces that rolled away back on the pile during reload. It is dirtier than running it normally, but the head output has been perfect. seems to only burn half way into the pile and take all day to reach and ignite the top. going to try and let it go late tonight since it was tended at 4am this morning as a test.

You may have a stove that is over sized for the job, but thats ok... Half loading the fire box as I saw in your picture may actually be worse than loading it and choking the primary air. In the case of half loading, primary air is able to go around the burning coal and go up the chimney which will starve the fire and make it very inefficient..

I agree with the others that reducing the firebox size or half loading is not the answer. Just load it as usual and choke down the primary combustion air to achieve a slower cooler burn. If you get to the point that your primary air is closed and there is still too much heat, then your gaskets may not be sealing tightly.. Try 24 hour tending schedule on warmer days. Many times on warmer days, its difficult to maintain a healthy draft in the chimney. I advise setting up a manometer to monitor draft. If you loose draft in the chimney the fire will go out due to no combustion air getting in (the two are directly related to each other) AND you run the risk of leaking carbon monoxide into the living area. When trying to achieve a low slow burn on warm days, cut back the primary combustion air to a sliver and give it more secondary air (over the fire air).. This extra over the fire air shouldn't increase combustion, but instead will just get heated and go up the chimney to help maintain a healthy draft.

On colder days when you want the heat, cut back secondary air and increase primary air since in this situation you don't want excessive heat going up the chimney.. You want it in your house

Hi Resolute0058I am on my second year burning coal with a Harman Mark 111 which is oversized for my application much of the year but at -22 the other week and a daytime temp of just above 0 I was very glad it was oversized and able to keep things very comfortable. Last spring I used your half load technique extremely successfully. The half load system worked significantly better than reducing the size of the fire box which I tried in the fall. A couple of differences.I left a 2 – 3 inch layer of ash on the cool side and did not touch the shaker handle for almost 4 weeks. No air got around the cool side.I burned 10 – 15 lbs of coal a day - Blaschak bagged pea.Ash pan dumping was every 4 days or so.All ash removal was done with a poker – hook from underneath and coal bridging was removed by poking from the top.Fire was on the right side and the Condor magnetic thermometer was above the door on the left side. It often read about 150 degrees. Could easily ramp up the output for the cooler nights. I was able to keep a very small hot fire with lots of stove surface area to increase efficiency.You can also reduce the ash removal area so you only get a nice glow about the size of a softball for further temp reduction and the fire still did not go out. This approach to lower output may not work in all stoves but was very effective for my application.No windowstats were required.

Days got to the upper 60’s but nights were cool. The Dwyer MK 2 permanently installed showed a draft of .01 or below at times and none of the co detectors went off. Draft was normally .06 during the winter.Good luck. Ken

Lisa has the same stove you have, so pay close attention to all she said. I'm especially curious about your stove surface temperature on the front, just above the door. If you have it down to about 180* and your house is still too hot, there's not much more you can do. Unless something is wrong you should be able to throttle it down to near that temperature with a FULL firebox and without re-engineering the stove or playing games with ashes.

I wonder if you have too much draft. Tell us more about your chimney and stovepipe. What kind of chimney, how tall from where the stovepipe enters, and does it go up through the interior of your house or is it all exposed outside? Do you have a barometric damper (you should); and do you have a manometer to see what draft you are getting? (I confess that I DON'T have a manometer -- I just set the baro to the lowest draft I can get away with, and still have the stove respond reasonably quickly when I open the inlet for more heat.)